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6 Dec 2010

Volume 97, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages)

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie
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CoIr-carbon complexes with magnetic anisotropies larger than 0.2 eV: A density-functional-theory prediction

Ruijuan Xiao, Michael D. Kuz’min, Klaus Koepernik, and Manuel Richter

Appl. Phys. Lett. 97, 232501 (2010); http://dx.doi.org/10.1063/1.3520488 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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We report a density-functional study of the heteronuclear CoIr dimer adsorbed on benzene or graphene. In either case, CoIr prefers an upright position above the center of a carbon hexagon with the Co atom next to it. The Ir atom stays away from the carbon ring and thus preserves its free-atom-like properties. This results in a very large magnetic anisotropy of more than 0.2 eV per dimer. So high a value should suffice for long-term data storage at the temperature of liquid nitrogen.
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75.30.Gw Magnetic anisotropy
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)

Intrinsic room temperature ferromagnetism in boron-doped ZnO

X. G. Xu, H. L. Yang, Y. Wu, D. L. Zhang, S. Z. Wu, J. Miao, Y. Jiang, X. B. Qin, X. Z. Cao, and B. Y. Wang

Appl. Phys. Lett. 97, 232502 (2010); http://dx.doi.org/10.1063/1.3524493 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2010

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We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1−xBxO films deposited under high oxygen pressure by pulsed laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonically from 0 to 1.5 emu/cm3 with the increasing boron component x from 0% to 6.8%. The first-principles calculations demonstrate that the ferromagnetism in the B-doped ZnO originates from the induced magnetic moment of oxygen atoms in the nearest neighbor sites to B–Zn vacancy pairs. The calculated total magnetic moment shows an increasing trend with the boron component which is consistent with experiment.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition

Single picojoule pulse switching of magnetization in ferromagnetic (Ga,Mn)As

A. H. M. Reid, G. V. Astakhov, A. V. Kimel, G. M. Schott, W. Ossau, K. Brunner, A. Kirilyuk, L. W. Molenkamp, and Th. Rasing

Appl. Phys. Lett. 97, 232503 (2010); http://dx.doi.org/10.1063/1.3524525 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2010

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The recently demonstrated photoinduced reduction of the coercive field in (Ga,Mn)As is shown to display a pronounced increase in efficiency when triggered by short laser pulses. This is due to the relaxation timescale of the effect that is measured to be about 1.5 ns. In addition, a single 100-fs-pulse with only 80 pJ of energy is found to be sufficient to write a magnetic domain.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Dd Nonmetallic ferromagnetic materials
78.47.J- Ultrafast spectroscopy (<1 psec)
75.50.Pp Magnetic semiconductors
78.66.Nk Insulators
78.20.Ls Magneto-optical effects

The peculiar magnetic property evolution along RCu3Mn4O12 (R = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu): A first-principles study

Xiaojuan Liu, Shuhui Lv, hongping Li, and Jian Meng

Appl. Phys. Lett. 97, 232504 (2010); http://dx.doi.org/10.1063/1.3524527 (3 pages)

Online Publication Date: 6 December 2010

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Within RCu3Mn4O12 (R = Rare earth), besides the expected ferrimagnetic order of Mn and Cu ions below TC1, R magnetic moments also play an important role at lower temperatures TC2, leading to their peculiar magnetic behavior. By first-principles calculation, we found that along the series from La to Lu, TC1 monotonically increased due to the ionic radius (IR) induced chemical pressure, as experimentally observed, while TC2 is closely related to the atomic radius of R. Additionally, the magnetic anisotropy energy (ΔEani) along the series is found to be correlated with the total magnetic moment of R ion.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics

Characteristics of a high temperature vertical spin valve

Debashish Basu, Hyun Kum, Pallab Bhattacharya, and Dipankar Saha

Appl. Phys. Lett. 97, 232505 (2010); http://dx.doi.org/10.1063/1.3524820 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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We demonstrate high temperature electrical spin injection and detection in degenerately p-doped GaAs in vertical spin valves using valence band electron tunneling. The maximum measured magnetoresistance at 10 and 300 K is 40% and ∼ 1%, respectively. Spin relaxation in these devices was found to be relatively insensitive to temperature (T) for T>125 K. The spin injection and detection efficiencies are mostly dominated by the ferromagnetic contact polarization and spin independent transport at the ferromagnet/semiconductor interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.-b Spin polarized transport
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Magnetic properties of full-Heusler alloy Co2Fe1−xMnxAl films grown by molecular-beam epitaxy

K. K. Meng, S. L. Wang, P. F. Xu, L. Chen, W. S. Yan, and J. H. Zhao

Appl. Phys. Lett. 97, 232506 (2010); http://dx.doi.org/10.1063/1.3525376 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2010

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We have investigated magnetic properties of single-crystalline full-Heusler alloy Co2Fe1−xMnxAl films (0<x<1) grown on GaAs (001) by molecular-beam epitaxy at different temperatures. It is found that as x increases, the films grown at 160 °C have complex magnetic phases, but show pure ferromagnetic properties when grown at 280 °C. We attribute this magnetic behavior to the competition between ferromagnetic and antiferromagnetic Mn–Mn interactions, which are proved by x-ray magnetic circular dichroism measurements. Moreover, we have investigated in-plane magnetic anisotropies of Co2Fe1−xMnxAl films with pure ferromagnetic phases and deduced the corresponding anisotropy constants which also remarkably depend on x.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Magnetization dynamics triggered by surface acoustic waves

S. Davis, A. Baruth, and S. Adenwalla

Appl. Phys. Lett. 97, 232507 (2010); http://dx.doi.org/10.1063/1.3521289 (3 pages)

Online Publication Date: 7 December 2010

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Investigations into fast magnetization switching are of both fundamental and technological interest. Here we present a low-power, remote method for strain driven magnetization switching. A surface acoustic wave propagates across an array of ferromagnetic elements, and the resultant strain switches the magnetization from the easy axis into the hard axis direction. Investigations as a function of applied magnetic field as well as unidirectional anisotropy (the exchange bias) reveal excellent agreement with prediction, confirming the viability of this method.
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75.78.-n Magnetization dynamics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
62.65.+k Acoustical properties of solids
68.35.Iv Acoustical properties

Ultrathin Co/Pt and Co/Pd superlattice films for MgO-based perpendicular magnetic tunnel junctions

K. Yakushiji, T. Saruya, H. Kubota, A. Fukushima, T. Nagahama, S. Yuasa, and K. Ando

Appl. Phys. Lett. 97, 232508 (2010); http://dx.doi.org/10.1063/1.3524230 (3 pages) | Cited 17 times

Online Publication Date: 9 December 2010

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Ultrathin [Co/Pt]n and [Co/Pd]n superlattice films consisting of 0.14–0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3–9)×106 ergs/cm3] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2–2.4 nm. The films were stable against annealing up to 370 °C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 Ω μm2) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.15.Cd Deposition by sputtering

Low loss superconducting titanium nitride coplanar waveguide resonators

M. R. Vissers, J. Gao, D. S. Wisbey, D. A. Hite, C. C. Tsuei, A. D. Corcoles, M. Steffen, and D. P. Pappas

Appl. Phys. Lett. 97, 232509 (2010); http://dx.doi.org/10.1063/1.3517252 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2010

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Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into rf coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e., high and low electric field regimes, respectively. At high field, we found the highest internal quality factors ( ∼ 107) were measured for TiN with predominantly a (200)-TiN orientation. The (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, ≈2 nm, layer of SiN during the predeposition procedure. On these surfaces we found a significant increase of Qi for both high and low electric field regimes.
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84.40.Az Waveguides, transmission lines, striplines
81.15.Cd Deposition by sputtering
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Enhancement of ferromagnetic properties in Zn0.95Co0.05O nanoparticles by indium codoping: An experimental and theoretical study

O. D. Jayakumar, C. Sudakar, C. Persson, H. G. Salunke, R. Naik, and A. K. Tyagi

Appl. Phys. Lett. 97, 232510 (2010); http://dx.doi.org/10.1063/1.3517450 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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Nanoparticles of Zn0.95−xCo0.05InxO (x = 0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When “In.” is codoped with Co with x = 0.0 to 0.07 in Zn0.95−xCo0.05InxO, a systematic increase in magnetic moment is observed up to x = 0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.50.-y Studies of specific magnetic materials
61.72.U- Doping and impurity implantation
75.30.Cr Saturation moments and magnetic susceptibilities
71.15.-m Methods of electronic structure calculations
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

The role of local anisotropy profiles at grain boundaries on the coercivity of Nd2Fe14B magnets

Gino Hrkac, Thomas G. Woodcock, Colin Freeman, Alexander Goncharov, Julian Dean, Thomas Schrefl, and Oliver Gutfleisch

Appl. Phys. Lett. 97, 232511 (2010); http://dx.doi.org/10.1063/1.3519906 (3 pages) | Cited 5 times

Online Publication Date: 10 December 2010

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We present numerical evidence from atomistic calculations that the coercivity of high-performance NdFeB-sintered-magnets (<20% of the theoretical Stoner–Wolfarth-limit) can be explained by a distorted region of Nd2Fe14B at grain boundaries, which has a reduced local magnetic anisotropy. We show that depending on the boundary composition of fcc-NdO and hcp-Nd2O3, the thickness of this region of reduced anisotropy varies between 0.4 for fcc and 1.6 nm for the hcp phase. For NdO, the distortions are mostly confined in the fcc-NdO-phase but equally distributes in both the hcp-Nd2O3 and Nd2Fe14B. The experimentally measured coercivity of 1.25 T can be understood when taking this distortion and magnetostatic effects into account.
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61.72.Mm Grain and twin boundaries
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets
75.30.Gw Magnetic anisotropy
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